1. Field of Invention
The present invention relates generally to AC/DC power converters and more particularly to a high efficiency AC/DC power converter operative to produce regulated DC output power with utility AC power as the input source.
2. Status of the Prior Art
In a conventional AC/DC converter, power is usually delivered to a DC load or multiple DC loads at a constant rate. Due to the fundamental nature of a single-phase AC source, power drawn from such a source has a pulsating nature with an average value equal to the output power plus losses incurred by the converter. Accordingly, the AC/DC converter must provide means for storing and retrieving energy during each half-cycle of the AC line.
In the conventional AC/DC converter, large value capacitors are used for energy storage. The voltage present on these capacitors determines the output voltage of the AC/DC converter and is regulated. In other words, the regulated output voltage of the AC/DC converter is a linear function of the capacitor voltage. When the conventional converter is used in universal input applications where the input line voltage can vary from 108 Vac to 264 Vac it is not feasible to maintain a regulated capacitor voltage. In order to mitigate the need for an AC/DC converter with a regulated output voltage and a wide range of input voltages, multiple AC/DC power converter designs have been developed. These are generally multiple designs of a dual power processing stage AC/DC converter. The first power processing stage is generally the voltage boost stage consisting of an AC rectified input followed by a choke-boosted converter. The choke-boosted converter has a capacitor output to provide for the energy storage described earlier.
The capacitor output presents an equivalent DC voltage source to the second power processing stage. The capacitor output, used for storing and retrieving energy, is generally a high capacitance capacitor or capacitors that are expensive and large in volume. The transformer turns ratio and the regulated output voltage of the first power processing stage defines the regulated output voltage of the AC/DC converter. The second power processing stage is a DC/DC converter with a transformer-rectified output.
In addition to providing regulated DC output voltage, the first power processing stage may provide for power factor correction (PFC). The second power processing stage accepts the regulated DC voltage from the first power processing stage and provides for input to output voltage amplification (via the transformer turns ratio) and galvanic isolation. Because of the large variations in utility voltages that exist in the global market place (i.e., 108 Vac to 264 Vac), a single conventional AC/DC converter design cannot process the full input voltage range and provide for the desired regulated output voltages. Accordingly, different converter designs are used to satisfy different portions of the input voltage range. As such, the AC/DC converter design for 120 Vac input will be different than that for 240 Vac input. Specifically, due to large variations in worldwide household and commercial AC power sources, multiple designs for the AC/DC converter are available. Furthermore, the desire for unity power factor by utility companies, the requirement for galvanic isolation for safety, and the large differences in application usage of power converter creates application specific designs. For example, conventional AC/DC power converters for battery chargers are designed for the specific application. The input voltage, as well as the output voltage requirements, are taken into considerations in the design process. Accordingly, the design of a conventional AC/DC converter for a given battery pack will change according to different AC input voltage sources.
The present invention addresses the above-mentioned deficiencies in AC/DC power converter designs by providing a single power converter design which can accept universal input voltages (i.e., 108 Vac to 264 Vac) and provide regulated DC output with a large voltage range. The invention is primarily an AC/DC power converter utilizing universal utility power to charge a battery pack. A battery pack is a group of batteries connected in series or series-parallel. The present invention operates using a single power processing stage, and provides power factor correction (PFC), input to output isolation (galvanic), and sine square output power. With the aid of relay(s) and a tapped transformer, the single stage AC/DC power converter of the present invention accepts input voltages of a global range (i.e., 108 Vac to 264 Vac) and provides regulated DC power with a large output voltage and power range capability, (i.e., 0 to 6 kW). The proposed invention provides constant power operation at large battery voltage range. For higher output power requirements, the multiple AC/DC power converters of the present invention can be operated in parallel or multiphase configuration without more effort than connecting the inputs and outputs accordingly. The AC/DC power converter of the present invention maintains a single design with higher efficiency, lower cost, and smaller volume than the conventional AC/DC power converters serving the same function.
In accordance with the present invention, there is provided a universal AC/DC power converter for generating regulated DC output power with large voltage range from a varying AC input voltage source of a global range (i.e., 108 Vac to 264 Vac). The AC/DC power converter has a single power processing stage, at least one relay in electrical communication with the output of the single power processing stage, a transformer in electrical communication with the relay, an output rectifier network in electrical communication with the output of the transformer, and a processor that contains the control for logic of the AC/DC power converter. The single power processing stage includes an input rectifier network to rectify the AC input voltage to a DC input voltage, and a voltage boost function to increase the DC input voltage to a higher regulated voltage defined herein as the boosted voltage. The boosted voltage is the regulated output voltage of the voltage boost function. The voltage boost function entails at least one inductor, at least one diode, at least four switching devices, an input current transducer, and the function of the processor. The four switching devices may be transistors such as power MOSFET""s or IGBT""s, and the input current transducer may be a sense resistor. In addition to the voltage boost function, the single power processing stage includes a voltage chop function that chops the boost voltage to form AC voltage. This AC voltage is in electrical communication with the transformer via the relays. The electrical components that make up the voltage chop function are some of the same components that make up the voltage boost function. For this reason the voltage boost function and the voltage chop function are defined as a single integrated power processing stage.
The relay (or relays) in electrical communication with the output of the single power processor stage is configured with at least two switching positions operated by the processor. The transformer (in electrical communication with the relays) has a primary winding and at least one secondary winding. The primary winding has at least two inputs operative to selectively vary the voltage generated on the secondary winding from the position of the relays. Alternatively, the relays can also be located on the secondary winding of the transformer without altering the intended function of the invention. Finally, an output rectifier network (in electrical communication with the transformer secondary winding) converts the AC voltage to DC voltage. The relays can selectively change the output DC voltage range of the AC/DC power converter by choosing the inputs of the transformer.
In accordance with the present invention, the AC/DC power converter includes a processor. The processor contains the control logic for the AC/DC power converter and may include a microprocessor and a power factor pre-regulator circuit. The processor is in electrical communication with the DC input voltage and the DC output voltage. The processor is operative to selectively position the relay or relays in response to the DC input voltage and the DC output voltage. In this sense, the processor directs the relays into a position that sets the AC/DC power converter into the proper output voltage range to charge a battery pack connected to its output. In addition to the DC input voltage and the DC output voltage, the processor may be in electrical communication with the input current transducer to perform the power factor correction function. The input current transducer may be a sense resistor or isolated current sensor. In addition to the processor, the sense resistor is in electrical communication with the switching devices and the input rectifier network. The processor also contains a logic circuit to perform the voltage boost function and the voltage chop function. In addition to the DC input voltage, the DC output voltage, and the input current transducer, the processor is in electrical communication with the output current transducer, and at least one external charge command to increase and regulate the DC input voltage to produce the boosted voltage. The output current transducer is also in electrical communication with the output rectifier network.
The processor is in electrical communication with the four switching devices. The four switching devices are modulated on and off by the processor in accordance with the external charge command for level charging, and for voltage, or current, or power modes of regulation. The processor may be preprogrammed to accept the DC input voltage data, input current data, output voltage data, output current data, and modulate the on and off time of the four switching devices to boost and regulate the DC input voltage as dictated by the external charge command for output voltage regulation, or output current regulation, or output power regulation.
The voltage chop function of the single power processing stage entails the four switching devices. The four switching devices are connected in an xe2x80x9cHxe2x80x9d bridge configuration and switched at a fixed frequency. During the voltage boost function the processor commands all four switching devices on for a portion of the period followed by turning off two of the switching devices for the remaining period. The two switching devices are two diagonal devices of the H-bridge. The processor determines the switching device operating duty for the voltage boost function. The duty is defined as the switching device on time divided by the on time plus the off time of the given period. The processor (in electrical communication with the external charge command, the DC input voltage, and DC output voltage) computes the duty for the four switching devices. As for the voltage chop function, the processor alternately sequences the diagonal switching devices of the xe2x80x9cHxe2x80x9d bridge on and off at a time when all four switches are not on. This complex switching sequence of the four switching devices will be described in more detail. The voltage boost function in conjunction with the voltage chop function boost the DC input voltage to a higher regulated voltage, herein defined as the boosted voltage and electrically chop it to form the AC voltage. The output of the single power processing stage is a regulated AC voltage with its amplitude consistent with the external charge command. This AC voltage is in electrical communication with the primary winding of a transformer via the relays. The inputs of the transformer may have primary inputs, tap inputs, or primary and tap inputs.
In the preferred embodiment, the AC/DC power converter is configured to produce regulated DC output power that is operative to charge at least one battery pack. In the preferred embodiment, the processor may be in electrical communication with the DC input voltage and the DC output voltage in order to determine the output voltage. The processor determines whether the inputs to the transformer should be the primary inputs, or tap inputs, or primary and tap inputs. As will be recognized by those of ordinary skill in the art, the transformer may include multiple taps for generating different secondary AC voltages therefrom and corresponding output DC voltages. The output rectifier network is in electrical communication with the secondary winding of the transformer. The transformer secondary AC voltage is rectified to form the DC output voltage.
In accordance with the present invention, there is provided a method of converting an unregulated AC input voltage into a regulated DC output with large voltage range, with an AC/DC power converter having a single power processing stage, at least one relay, a transformer with multiple inputs, an output rectifier network, and an output current transducer. The method comprises applying an unregulated AC input voltage to the input rectifier network of the single power processing stage to produce an unregulated DC input voltage. The unregulated DC input voltage is applied to a voltage boost function of the single power processing stage. The voltage boost function boosts the unregulated DC input voltage to form a regulated boosted voltage defined as the boosted voltage. A voltage chop function of the single power processing stage applies the boosted voltage to the input of the transformer via the relay(s) in an alternating sequence accomplished by sequentially switching the four switching devices. The result is the single power processing stage generates a regulated AC voltage output via the relays to the input of the transformer. The relay(s) select the transformer inputs for the application of the regulated AC voltage. The four switching devices are in electrical communication with the relay(s) and are operative by the processor. The processor modulates the on and off time of the four switching devices. With the four switching devices being modulated, the voltage to the input of the transformer is a regulated AC voltage. This regulated AC voltage is induced into the secondary winding of the same transformer. The output rectifier network is in electrical communication with the secondary winding of the transformer. The regulated AC voltage induced onto the transformer secondary is rectified by the output rectifier network to form a regulated DC voltage that is the AC/DC power converter output. Depending on the external charge command (in electrical communication with the processor), the AC/DC power converter output may be voltage regulated, current regulated, or power regulated.